A key sequence in director Roland Emmerich’s 2012 features the eruption of Yellowstone National Park as the stars of the film flee via a Winnebago and, eventually, by plane. Previs for this ‘Yellowstone’ sequence was undertaken by Image Engine in collaboration with the film’s overall visual effects supervisors Volker Engel and Marc Weigert. Image Engine’s previs technical supervisor Cameron Widen and VFX executive producer Shawn Walsh talk to vfxblog about their work for the sequence and about their previs philosophy.